The mechanisms of action of gonadotropin releasing hormone (GnRH) are being studied using both purified preparations of pituitary plasma membranes, and isolated cultured rat anterior pituitary cells. Plasma membranes are used to study the number and affinity of GnRH receptors, and to determine whether alterations in receptor characteristics occur in different physiological situations. Enzymes capable of degrading native GnRH have been shown to be associated with pituitary plasma membranes and the possible physiological role of these enzymes are being studied. Isolated pituitary cells in culture are used to study LH and FSH release in response to GnRH induced gonadotropin release are assessed following culture of the cells in the presence or absence of steroid hormones. In this manner the effects of steroid hormones at the level of the anterior pituitary cell can be delineated. Similarly the possible role of cyclic adenosine monophosphate (cAMP) in GnRH action can be determined by measurement of intracellular cAMP levels and correlation of cAMP changes with gonadotropin release.